The French Connection: The First Large Population-Based Contact Survey in France Relevant for the Spread of Infectious Diseases

Abstract

Background: Empirical social contact patterns are essential to understand the spread of infectious diseases. To date, no such data existed for France. Although infectious diseases are frequently seasonal, the temporal variation of contact patterns has not been documented hitherto.

Methods: COMES-F is the first French large-scale population survey, carried out over 3 different periods (February-March, April, April-May) with some participants common to the first and the last period. Participants described their contacts for 2 consecutive days, and reported separately on professional contacts when typically over 20 per day.

Results: 2033 participants reported 38 881 contacts (weighted median [first quartile-third quartile]: 8[5-14] per day), and 54 378 contacts with supplementary professional contacts (9[5-17]). Contrary to age, gender, household size, holidays, weekend and occupation, period of the year had little influence on the number of contacts or the mixing patterns. Contact patterns were highly assortative with age, irrespective of the location of the contact, and gender, with women having 8% more contacts than men. Although most contacts occurred at home and at school, the inclusion of professional contacts modified the structure of the mixing patterns. Holidays and weekends reduced dramatically the number of contacts, and as proxies for school closure, reduced R0 by 33% and 28%, respectively. Thus, school closures could have an important impact on the spread of close contact infections in France.

Conclusions: Despite no clear evidence for temporal variation, trends suggest that more studies are needed. Age and gender were found important determinants of the mixing patterns. Gender differences in mixing patterns might help explain gender differences in the epidemiology of infectious diseases.

Fig 1. Timeline of the study, showing the distribution of participants and contacts over time.

The periods of inclusion were February, 20^th–March,17^th; April,1^st–April, 7^th; April,16^th–May, 14^th. The dot size is proportional to the log of participant’s number. (Design Period 1: 34 days; Design Period 2: 29 days)

Fig 2. Contact number density.

Histogram of the contact number, including SPC (Supplementary Professional Contacts). Limitation at 40 contacts per day explains the peak at 40 contacts.

Fig 3. Degree distribution of children <4y, comparing number of contacts between <1y to 1–3y, with density of number of contact.

Similar graph with frequency of number of contact is provided as supplementary material S3 Fig.

Fig 4. Degree distribution comparing number of contacts according to gender in <18y and >18y, with density of number of contact.

Similar graph with frequency of number of contact is provided as supplementary material S3 Fig.

Fig 5. Degree distribution comparing number of contacts according to weekends and holidays in children (3–18y) and adults, with density of number of contact.

Similar graph with frequency of number of contact is provided as supplementary material S3 Fig.

Fig 6. Characteristics of contact (without SPC).

Distribution of location, duration and frequency for all contacts (A) and physical contacts (B). Duration of contact according to frequency (C). Proportion of physical contacts according to duration (D), frequency (E) and location (F).

Fig 7. 3D representation of the base-case matrix without SPC (Supplementary Professional Contacts).

Fig 8. Smoothed contact matrices without SPC, for physical contacts only and with SPC(Supplementary Professional Contacts) (right).

Relative incidence of a new emerging infection in a completely susceptible population estimated from the matrix in regard (left).

Fig 9. Smoothed contact matrices according to Actual Period (right).

Relative incidence of a new emerging infection in a completely susceptible population estimated from the matrix in regard (left).

Fig 10. Contact matrices according to location.

Numbers are the ratio of contact rate with contact rate at home (95%CI). No smoothing or reciprocity was applied (particular location wouldn’t be the same for a participant and a contact (e.g., at home vs. not at home), the matrices were kept asymmetric).